ORIGINAL RESEARCH Influence of cotton waste and flame-retardant additives on the mechanical, thermal, and flammability properties of phenolic novolac epoxy composites Suheyla Kocaman . Ulku Soydal . Gulnare Ahmetli Received: 8 April 2021 / Accepted: 19 June 2021 / Published online: 1 July 2021 Ó The Author(s), under exclusive licence to Springer Nature B.V. 2021 Abstract Phenolic novolac-type epoxy (EPN) resin composites were fabricated by reinforcing with cotton waste (CtW), along with aluminum hydroxide (AH), and boric acid (BA) particles under different filler loadings. For characterization, thermogravimetric analysis, scanning electron microscopy, differential scanning calorimetry, and water sorption tests were performed on the composites. The effects of the CtW, AH, and BA contents on the thermal, flame-retardant, and mechanical properties of the composites were investigated. The triple hybrid additive (CtW:BA:AH) with a ratio of 20:5:10 wt% exhibited the best mechanical and combustion properties. The tensile strengths of this composite and the neat EPN were determined as 95.7 ± 6.92 and 96.6 ± 4.77 MPa, respectively. The T 50 temperatures of the BA- and AH-doped composites were higher than that of neat EPN. The highest char percentages were observed in the triple composites, while the lowest were observed in the EPN/CtW composites. The combustion of the triple composite with a CtW:BA:AH ratio of 20:5:10 wt% was spontaneously extinguished in 37 s. Hori- zontal flammability testing also showed better fire resistance for the CtW/BA/AH composites over their CtW counterparts, with the highest estimated limiting oxygen index of 32.3 obtained for the 20:5:10 wt% composite. The water sorption test results show that the CtW composites had the highest hydrophilicity, especially those with 30 wt% CtW or higher, in the presence of water at room temperature. S. Kocaman (&) Á G. Ahmetli Department of Chemical Engineering, Faculty of Engineering and Natural Sciences, Konya Technical University, 42250 Konya, Turkey e-mail: skocaman@ktun.edu.tr G. Ahmetli e-mail: gahmetli@ktun.edu.tr U. Soydal Karapınar Aydog ˘anlar Vocational School, Selcuk University, Konya, Turkey e-mail: usoydal@selcuk.edu.tr U. Soydal Department of Biochemistry, Faculty of Science, Selcuk University, Campus, Konya, Turkey 123 Cellulose (2021) 28:7765–7780 https://doi.org/10.1007/s10570-021-04037-9